In 1972, the National Institutes of Health in collaboration with the Immunology Branch of the National Cancer Institute initiated a program to develop a highly inbred animal model suitable for tissue transplantation. The miniature pig was used and from its inception the experimental herd traditionally experienced conception rates and litter sizes considerably less than values reported for outbred, standard-sized pigs. To determine the causes of poor fertility and reduced reproductive performance, ovarian-endocrine relationships have been characterized in the miniature pig by studying reproductive hormonal profiles and ovarian morphology. The data have suggested that the reduced litter size in this particular strain is due to a deficient ovulation rate, potentially related to genetically altered endocrine function. Furthermore, ovulation number can be improved by gonadotropic therapy used in concert with synthetic steroids for synchronizing the reproductive cycle. Viable appearing embryos are detected following copulation; however, conception rates are reduced, probably due to a high incidence of cystic endometrial hyperplasia. As a consequence, this strain of miniature pig has proven to be a model for studying the adverse effects of increased homozygosity on altered reproductive/endocrine function and intra-uterine environment.